1. Field of the Invention
The present invention relates to a simplified and improved process for the preparation of 3-methoxy-4,5-methylenedioxybenzaldehyde and, more especially, to such simplified/improved process employing a 4,5-dihydroxy-3methoxybenzaldehyde (or hydroxyvanillin) starting material.
2. Description of the Prior Art
3-Methoxy-4,5-methylenedioxybenzaldehyde is known to this art as a very important compound which is a useful intermediate for the synthesis of many alkaloids, pharmaceutical precursors and pharmaceuticals, per se.
Various techniques for the synthesis of 3-methoxy-4,5-methylenedioxybenzaldehyde have been proposed to the art.
Among the most recent, the following methods of preparation are representative:
An article in the Bulletin of Chemical Society Japan (Matsumoto, 1985, 58 (1), pages 346 to 351) describes a process which firstly consists in preparing methyl 4,5-methylenedioxy-3-methoxybenzoate by reacting dibromomethane with methyl 4,5-dihydroxy-3-methoxybenzoate and then in reducing the ester group into a CH.sub.2 OH group with lithium aluminum hydride and, finally, in oxidizing this primary alcohol group thus created into an aldehyde group. According to the article, the overall yield of this three-stage synthesis is 57%. This process is far too complicated and the productivity thereof is too low for it to be employed industrially.
In an article in Chemische Zeitung (Dallacker 1984, 108, (5) pages 186-187), another preparative method is described. It consists in starting with 4,5-methylenedioxy-3-methoxyaniline in order to form 5-bromo-1,2-methylenedioxy-3-methoxybenzene; the bromine is then replaced by an aldehyde group. The overall yield of this synthesis is approximately 37%. Like the above process, this process is complicated and the productivity thereof is too low for it to be employed on an industrial scale.
Another article in Journal of Chemical Society Perkin Trans. (1, 1984 (4) pages 709-712 by McKiftrick and R. Stevenson) describes a procedure which forms a methylenedioxy bridge on hydroxyvanillin. The reaction between hydroxyvanillin and dibromomethane in the presence of potassium carbonate is carried out in dimethyl sulfoxide. As the recovery of the final product requires a treatment with water, this makes the recycling of the very expensive solvent difficult. No yield is specified.
The processes of the prior art typically entail the formation of the aldehyde group in the final stage; the process mentioned immediately above, which consists in forming a methylenedioxy bridge on a compound already bearing an aldehyde substituent, employs a solvent which is expensive and difficult to recycle.